2.1. Study population

This study involved participants of the JPHC study, which was launched in 1990 (Cohort I) and 1993 (Cohort II). ²⁹ At the baseline survey, individuals aged 40–69 years who lived in 11 public health center areas were recruited. Participants reported their medical and family histories and health‐related lifestyles via self‐administered questionnaire surveys. The questionnaire surveys were conducted three times every 5 years from the baseline survey.

As the second (5‐year follow‐up) questionnaire survey asked for more detailed information on nutrient and food intakes compared with the first survey, we considered data from the second survey in 1995–1999 as the baseline data in this analysis. Participants were informed of the objectives of the JPHC study and that completion of the second questionnaire was regarded as providing consent to participate. Of individuals who participated in the second survey (n = 98,469), we excluded those who answered that they were diagnosed with cancer before the second survey (n = 1614), those with missing values for nutrients (n = 1063), and those with an extremely high or low intake of total energy (above the 97.5th percentile or below the 2.5th percentile of total energy intake according to sex) (n = 4787). A final total of 91,005 participants (men: n = 42,405 and women: n = 48,600) were included in the current analysis.

This study was approved by the Institutional Review Board of the National Cancer Center of Japan (approval no. 2015‐085) and was conducted following the ethical guidelines for medical research in Japan.